To my understanding, they start with basic math, and go up through linear alegbra and such. The website seems to have sample chapters for every level, which might help you. I bought "Apples", and it starts with basic addition concepts.

Which ones? As the PP noted, Fred books go from 1st grade up through college level (Calc, Stats, and Linear Algebra).

There is a difference in usage between the two series (elementary series is most useful if done with a parent; for most students, Fractions on up is most effective is the student works independently-- as long as they take their time and actually work it rather than racing through. There is quite a lot of math in both series!).

Life of Fred Fractions and Decimals are for whenever your dc has completely mastered long division - 5th grade is a suggestion, but could be sooner.

The Life of Fred Elementary series is kind of tough to classify. We're just starting Dogs, so I can only speak for the books up to this point. It has very basic math (addition, skip-counting, place value, etc.), but it has a lot of other "stuff" in it - math concepts, such as sets, infinity, natural numbers, etc. which are higher level. Also lots of other things, from geography to grammar to geometry concepts. It does show from day one how addition is related to algebra - I love this, I think algebra will not be intimidating at all with this kind of an introduction.

So I can say that DD9 has not run into any math that she cannot easily do, but I still think it has been worth it for her. It is the kind of learning she thrives on - word based, story based, a little silly, but very engaging.

DD5, on the other hand, while she gets the math just fine, is not really mature or experienced enough to get the story elements, so I think she finds it a little weird. I started Apples with her, but I've decided to put it away for a year and maybe try again in 1st grade. Again, not that the math is too hard, on the contrary, but I think she just doesn't "get" it yet, so the benefit of the stories is kind of wasted on her at this point.

OH my goodness. I didn't realize how many books there were!! I knew about the apples and the 4 after that, but now there are like 8 or something!! I think something Pre-fractions/decimals/percents would be good for my kids, but not sure where to start?? its crazy how some of these things make you want to start from the beginning, even though they are over that level lol

These are our "I need a break" math and our " Summer" math program. We love them. Ds grade 2 flew through Apples and Butterflies...and is working through Cats. My 4th grader is doing Dogs. Dd 13 has used Fractions and Decimals...and will be using both Pre-Algebra programs over the summer.